I am hoping to get some Checkerboard cichlids for my 200 l aquarium. It has a length of 100cm, a temperature of 27.5°C and an oversized filter. The substrate is silver sand, and it’s heavily planted, with bogwood and branches and a few rocks, leaf litter and Savu pods. The pH is 6.8–7 — I use tapwater, but there are peat granules in the filter. Water changes are carried out every two weeks, meaning nitrate and nitrite is always low. Lighting is quite dim, but there are floating plants.

If Checkerboard cichlids are suitable, would you recommend a pair or harem?

SAM PUTNAM, EMAIL

The Dicrossus filamentosus in the trade have usually been bred in the Czech Republic. Image by Svenska, Creative Commons.

That sounds like a great set-up for Checkerboard cichlids! There are two species — Dicrossus maculatus with the heavier checkerboard pattern on its body and shorter fins, and D. filamentosus, with that beautiful lyretail. D. maculatus are the cheaper of the two and usually come in wild caught, while D. filamentosus commands a premium and isbred in the Czech Republic by suppliersof Apistogramma.

Both will come in small and not looking like they do in the pictures, but give them the right conditions, like it sounds like you have in your tank, and they will thrive.

Juveniles will not be easy to sex so start with a group, with the aim of eventually obtaining a pair. Juveniles do shoal in the wild so will get on fine, but once those males hit 5cm and start to colour up they will want a space all of their own, and I would only look to keep an adult pair in a tank of your size long term. JEREMY GAY

I have a tank containing a five-year-old Musk turtle (it only eats worms and pellets). Could I keep a Hairy puffer in the same aquarium?

KITTY JACKSON, EMAIL

Assuming you’re talking aboutTetraodon baileyi, this species is a lot like other ‘lurker’ pufferfish in preferring habitats with brisk currents and plenty of oxygen. They like to lurk among smooth pebbles and driftwood, where their cryptic colouring helps them to blend in. While they don’t move about much, when prey does move into view, they can accelerate rapidly enough to snap up small fish and crustaceans that get too close to them. Because they are relatively inactive they can be kept in fairly modest aquaria: an adult specimen around the 10cm mark will be perfectly content in a well-filtered and well-maintained 90 l tank.

Their modest requirements have made them popular with people interested in oddballs. Buying a single tank and all the accessories won’t be too expensive, and water changes will be quick to do, which is important for fish that are both greedy and very sensitive to high nitrate levels.

Musk turtles are nice little beasties, but like all turtles they’re not compatible with aquarium fish. Turtles are heavy polluters which means that the water in their tanks rarely has zero ammonia and nitrite values, and nitrate levels rise alarmingly between water changes because of the sheer quantity of food given to them. So while you might see fish and fully aquatic turtles combined in public aquaria, it’s almost never practical to do in thehome aquarium.

In addition, pufferfish tend to be snappy, with a bite-it-and-see approach to finding food. While I doubt even an adult puffer will be able to crack through the shell of your Musk turtle, the flippers and tail are a bit more vulnerable.

So I’m afraid that I really wouldn’t recommend that you mix the two.NEALE MONKS

Slime molds feed on decaying organic matter, so their presence can indicate a problem. Image by Luke Glover.

I recently set up a planted Fluval Edge 23 l/5 gal tank, after a few weeks and some new occupants later I noticed this ‘creature’, which I’ve since discovered could be an aquatic slime mold — but that’s where the info ends unless you understand scientific talk.

It seems to move around the tank, along the wood, occasionally disappearing into the substrate. Whilst I never see movement, if left for a period of time it will have relocated to another part of the tank.

For now, I’ve manually removed it with a syphon and toothbrush. But where did it come from and how do I stop it coming back? LUKE GLOVER, EMAIL

Slime molds — those that are big enough to see, at least — are uncommon in aquaria, though small colonies could easily go unnoticed, so it’s hard to say whether or not they’re a normal part of freshwater set-ups.

What we can say is that they’re a bit like fungi in habits, consuming organic matter such as decaying plant material. That being the case, they’re not likely to threaten your fish directly. but just like fungi, they are a sign that’s something amiss with the aquarium. If you can see slime molds or tufts of fungi, there’s something in the tank decaying that they’re digesting. In doing so they’re producing waste products that the filter has to deal with, ultimately raising nitrate levels between water changes.

The fact that your tank is very small highlights some possibilities. A deep substrate can be very good at accumulating debris that the slime mold could be feeding on. It’s also very easy to overstock a small aquarium or overfeed the tank residents, and the faeces and uneaten food will provide food for your slime mold.

The one time I’ve dealt with slime molds in an aquarium was after adding fresh wood as decoration, as opposed to cured bogwood. Again, organic material in the wood provided food for the slime molds.

A lack of water circulation can also prevent organic debris from ending up in the filter where it can be processed by the bacteria, providing more food for the slime mold. NEALE MONKS

I have just got into fishkeeping and I have a 40 l/11 gal tropical tank that currently has two Serpae tetra in it. I was wondering what tank mates I could add as everything I have read about them has told me they are quite dominant. I would like some colourful mid to top dwellers if possible.DANIEL FAIRLIE, EMAIL

Serpae tetra, Hyphessobrycon eques, do indeed have a somewhat deserved reputation as pugnacious, ‘nippy’ fish and will often dominate and bully less robust species. The best way to lessen the chances of this occurring is to stock them in larger numbers; I would recommend a bare minimum of ten but even then they may still be a problem with some fish. Unfortunately, your tank is too small for this as these active fish can reach 4cm/1.6in long.

Ember tetra, Hyphessobrycon amandae.

My recommendation would be to return your two existing fish to the shop you bought them from, and replace them with a group of at least six Ember tetra, Hyphessobrycon amandae, which share similar burnt orange colouration, but typically grow about half the size and are not aggressive like the Serpaes.

Adding some hardy live plants such as Cryptocoryne and Anubias will provide more cover and bring out better colour in your fish, and then perhaps you could consider a few Sparkling gourami, Trichopsis pumila, to fill the upper layers (add some floating plants if you do) and maybe a group of five Kuhli loach, Pangio semicincta, for the bottom. BOB MEHEN

I have a real problem with pulsing Xenia in my tank. I constantly cut it off and ensure everything comes out but it just grows back. It is now starting to affect my SPS corals and clam. Is there a way to get rid of it that won’t involve stripping the tank down? The only thing it won’t grow up against is my Palythoa colony which seems to burn it back. Help!LUKE, PORTSMOUTH

Pulsing Xenia can look fabulous, but at the same time it can become invasive, attaining weed-like status in many aquariums. It can shade out other sessile invertebrates and outcompete them for space, but studies have shown that xeniids also emit toxic (‘allelopathic’) chemicals which can harm neighbouring corals. Unfortunately, controlling it can be difficult, although it’s possible to confine it to specific areas of the aquarium (at least to a certain extent) by keeping it on isolated rocks away from other invertebrates. This can help curtail its spread throughout the aquarium. Biological control is hit-or-miss at best, and chemical control can work, but it runs the risk of polluting the aquarium as the Xenia dies off, so physical control is the best approach.

As far as removing the existing Xenia, bear in mind that they’re very good at regenerating from even the tiniest fragment left behind. Therefore, simply cutting them off at the base, or even scrubbing them off the rocks can leave tissue behind, allowing them to regrow.

Where possible and practical, look into completely removing the worst-affected rocks and trade these with other aquarists or your local fish shop (someone will actually want them!). Otherwise, you’ll need to temporarily remove the rocks and physically remove the entire colony before replacing them. This means either chiselling or snipping away at the rock on which the Xenia is growing with a suitable tool (avoid getting any oil in the water from the tools, and wash them straight after use). On rocks that you can’t lift out of the water, this will be trickier, but it can still be done. Xenia that’s growing on the glass can be simply scraped off with a credit card or metal blade, but do this whilst syphoning at the same time to remove the animal.

A complementary approach is to try and limit nutrients. Xenia don’t actually feed (they don’t have a functional gut or mouthparts), but they can take up nutrients directly from the water, so elevated phosphate and nitrate could encourage their growth. Having said that, some folks with pristine aquarium water still find Xenia a problem, but this is certainly worth looking into all the same. Ensure mechanical and chemical filtration (activated carbon and phosphate-adsorbing media) are working effectively, and the protein skimmer is suitably adjusted to pull out maximum organics from the water. DAVE WOLFENDEN

Airstones oxygenate the water, but the pumps running them can be noisy.

My air pump is very noisy and non-fishkeeping family members are complaining. How can I make it quieter? It has a really annoying rattle and hum noise, which is upsetting the peace of my aquarium.MATT FLYNN, EMAIL

Some air pumps are quieter than others so that may be the first factor. The second is the power of the pump. Larger air pumps generally make noise than smaller ones.

What airline are you using? Clear PVC 6mm airline is the most common although it can get brittle over time, causing rattling if it touches and vibrates against a cabinet wall. It also becomes stiffer, causing your pump to ‘walk’ across a space until it hits a cabinet wall and itself cause lots of noise and vibration. If using PVC, swap for soft silicone airline.

Non-return valves cause back pressure and noise, but you definitely need these. Some are more supple than others though, which I test by blowing through them to see which one allows airflow the easiest. Try new airline and a new valve, and check that the air filter pad isn’t blocked or restricted.

Where the pump is situated can also be a factor. A cabinet can act like a speaker box, amplifying noise. Try placing a Tupperware container over the pump with a gap underneath to allow air in.

Many air pumps also have provision for vertical mounting, so try that if possible — or you could even hang it with string. Take the contact with hard surfaces away and any noise should be reduced dramatically. JEREMY GAY

I have a TMC 60 l reef set-up with LPS, mushrooms and polyps. It has a nano skimmer and the supplied lighting. It houses one Gobiodon okinawae, a hermit and a Peppermint shrimp and contains live rock. It was set up in January but over the last month I’ve been getting slime algae on the rocks and substrate. I syphon it off but it comes back in a day or two. I use Rowaphos and carbon and RO water, bought ready salted from my local store. I only use fresh RO for top-ups. The tank has the supplied powerhead, but would adding another be beneficial to increase circulation? I feed a small amount every day and occasionally add live copepods or brine shrimp. Any ideas?P. W. ROSE, LINCS.

Slime ‘algae’ (usually cyanobacteria) is invariably caused by high nutrients — with nitrate and phosphate being key factors to look at. Limit these and you can solve the problem. You should be looking at less than 0.03ppm phosphate and 5ppm nitrate or less. Both of these parameters, or a combination of them, is likely to be the issue.

Look at how to limit nutrient input to the system. See if you can cut back on feeding, even slightly. Then, embark on a programme of exporting nutrients. This will include increasing the frequency of water changes (it’s worth checking your salt water and RO water parameters, too), coupled with continued syphoning of the slime — keep up with this. Clean your mechanical filter media on a daily basis to remove detritus (and perhaps look to increase the efficiency of mechanical filtration through the use of additional fine floss or foam). If you’re getting phosphate above 0.03ppm, change the Rowaphos or review how it’s used, as it may need repositioning to ensure it’s working at maximum efficiency. Check the skimmer is operating efficiently by cleaning and adjusting it accordingly.

Increasing water movement is a good idea, as it will help to remove dead spots, assisting with physically dislodging the cyano as well as the detritus which may settle out and act as food for it, allowing both to be taken through the mechanical filter. In fact increasing water movement is often all that’s needed to solve the problem.DAVE WOLFENDEN

Suckermouthed plecs are poorly suited to life in a mbuna set-up. Image by MP & C Piednoir, Aquapress.com

Strictly speaking there aren’t any suckermouthed catfish in Malawi cichlid habitats. so I would leave them out. There is an African species called Chiloglanis, although this is a river fish, not a deep lake fish, and it’s not easy to keep by any means. Don’t opt for them.

That leaves you with South America and Asia. Any wild caught L-number will be unsuitable because of their preference for soft acidic water and once the algae has gone you won’t be able to feed them. Your Africans will eat any algae wafer you drop in and the plecs are likely to starve.

From Asia there are the hillstream loaches — again specialist stream fish and sensitive — Garra spp., which are tougher but will be outcompeted and are not all biotope correct. There is one species though, Gyrinocheilus aymonieri, which is the bane of many tropical fishkeepers’ lives. It is a good algae eater but becomes territorial as it grows, much like Malawi cichlids, so is often returned to the shop for being a nuisance.

If you could get a 10–15cm/4–6in specimen which has been returned to a shop it would be tough enough to put up with your cichlids, carve out a living eating algae and give as good as it gets in terms of squabbles.

There is a tank bred suckermouth option, and that is the generic bristlenose catfish — the type which you see regularly for sale as small juveniles. My friend added some to his large mbuna tank 11 years ago and they are still there to this day. They are now large adults and in good condition, although the lack of suitable Malawi cichlid proof caves means that he has never had fry from what are usually very prolific breeders. That, or the hard water is preventing them from breeding.

So if you have to, tank bred bristlenoses or adolescent to adult Gyrinocheilus are your best options, although it will be a compromise in terms of water hardness and feeding any extra foods will prove difficult.

Some Malawi cichlids are better grazers than others. The best are probably Labeotropheus, followed by Petrotilapia and Tropheops, although no cichlid will remove the green from your front glass. Use an algae magnet or scouring pad for that.JEREMY GAY

What’s the best number of firefish to keep in a group? I have a 400 l/88 gal set-up which has been running now for three months. Will it be mature enough to add a group of these? The tank also houses a pair of Black percula clowns and I aim to add a Yellow tang, a Flame angel and possibly a Royal gramma later on.CHARLIE NOAKES, EMAIL

Firefish (Nemateleotris spp.) can actually be very tricky to keep in groups — although they are often seen in groups on the reef (making them appear social), they can be aggressive with each other in the confines of the aquarium, and weaker individuals can be harassed to the point of death by one or two dominant fish. Don’t be fooled by the groups of them you may see in the shop’s holding tanks — the fish don’t spend enough time in the tanks, or have sufficient territory to defend, to show their true behaviour. This is a shame, as groups of firefish look stunning in the wild, but it’s hit-or-miss trying to replicate this in the aquarium. It can be done (and having plenty of room makes things easier) but the best way to keep them is one individual fish or an established pair (if you’re lucky enough to get one).

The Zebra dartfish is a closely related species to the firefish, and it can be kept in groups in the aquarium.

Why not consider the closely-related dartfish (Ptereleotris spp.) if you’re looking for a more social species? These fish have similar behaviours, and some species can be kept in social groups, which can look amazing. I’m going to plug the Zebra dartfish, P. zebra, (up to 10cm/4in) here, a lovely-looking and readily-available fish which does very well in groups of several individuals; in a 400 l/88 gal system, you should be looking to keep five or more of these fish, added all at the same time. Their feeding requirements are the same as for firefish — frequent feeds of small items are needed for these planktivores.

Bear in mind that all firefish and dartfish are superb jumpers, so a covered aquarium is recommended, and they require a sandy area and plenty of hiding places.DAVE WOLFENDEN

I've learnt the hard way that you really can't afford to skimp on quarantining new fish!

I have a heavily planted 120 l tank with around 15 Amano and Red cherry shrimp, five false Julie corys and one surviving Fork tailed blue eye. The blue eye was once one of eight along with two elderly but much loved guppies — until I was foolish enough to add a few more blue eyes straight into the tank.

Fairly early on it seemed that two of the new fish weren't happy and seemed to not be eating. Then came a period of regularly dead fish and much desperate searching for cause and diagnose.

Eventually we realised we had Camallanus worms. Treatment seems to be a nightmare and the Internet is full of confusion, with lots of sites recommending treatments that don't seem to be available in the UK or advising bird dewormers which I'm hesitant about.

I understand the dewormer would kill my shrimp and some sources seem to say corys might struggle too. Should I move the shrimp and risk the corys (they don't seem to have any signs of infection)? Can the shrimp carry the infestation and re infect the tank? Is there a different medicine I should be using? JENNY MARCHANT, EMAIL

You don’t mention how you arrived at your diagnosis of Camallanus. Diagnosis requires the observation of one or more red-brown worms (up to 2cm/0.8in long) protruding from the fish’s vent, or the discovery of the worms within the gut of a dead fish.

Camallanus worms in the gut of a fish.

Assuming you have observed the actual worms, then we need to consider a few points about Camallanus infections: there are several species of Camallanus and they infest various freshwater fishes, including guppies. Living within the fish’s gut, these worms remain out of sight — so you may not have detected them even if you had quarantined your new fish (although quarantine is always a good idea). Generally, it is only when one or more female worms protrude from the fish’s vent to shed their larvae that a Camallanus problem is discovered. Low numbers of worms in the gut may cause no obvious disease signs but heavy infestations can lead to body wastage and can be fatal.

Fish acquire Camallanus through eating worm-infested copepods (tiny crustacean relatives of water-fleas, sometimes sold as live food). In the case of Camallanus cotti (which infests guppies, Betta, and other species), some experts believe that fish can additionally pick up this worm directly, by ingesting free-living worm larvae in the water. There is no evidence, to my knowledge, that shrimps will harbour Camallanus.

As for treatment — and this assumes you have a confirmed diagnosis of Camallanus — I would choose one of the commercial fish wormers that contains either Flubendazole or Fenbendazole as the active ingredient. These wormers are reportedly toxic to shrimps so you will, unfortunately, have to treat all your fish (including the corys) in an isolation tank — I suggest isolating them for four weeks. You may need to re-dose every week or so during this isolation period — but follow the manufacturer’s instructions. DR PETER BURGESS

We've heard of several cases where pondfish have been eaten by otters. Image by Shutterstock.

Yesterday we woke to find 10 very large Koi up to 50cm/20in length dead and half eaten, spread around the garden. Our pond is 48in/4ft deep with no shelf. It has an overflow drain that drains into a culvert and we noticed the cover was off.

We live just outside Much Wenlock in Shropshire and we have no idea what could have done this. Any ideas?DIANE CLIFTON, EMAIL

Sorry to hear you’ve had this problem. I spoke to a carp angling, carp keeper and he had this to say when I asked him if it was an otter:

“Half eaten is classic otter. I have seen carp on my lake with just the stomachs eaten.

“This is a massive problem with otters being introduced into areas. They eat nesting birds, rare amphibians too.

“They are an apex predator, like a wolf in a field of sheep. People can’t shoot them as they are protected.”

So it’s an otter. Standard netting won’t keep them out and they can and will come back. I’d rather otter roamed the UK’s waterways than introduced mink, and one could argue that there are plenty carp to go around, both in ornamental ponds and fishing lakes.

Not you want to hear though and you must be absolutely gutted. As mentioned above you can’t touch them so your only way is to try to prevent them entering the pond, and that probably means strong wire mesh or a metal grid system. JEREMY GAY

If you are finding too much food is reaching the bottom before the fish have chance to eat it, try adding a little at a time rather than feeding it all at once.

I am new to fishkeeping and I recently tried a food claimed to feed fish at different levels in the aquarium. When I added it most of it went straight down to the bottom of the tank due to the flow of the water. Is there a way to stop it sinking so quickly? Is it better if I turn my filter off when I feed the fish?G. REES, EMAIL

It really depends on what type of filter you have and how you position it.

Most internal filters return water to the tank horizontally, which should produce a flow across the tank, (and often weakly back again toward the filter as the flow deflects off the opposite side). This should mean that any sinking food added will remain suspended in the water column for a short time as it sinks.

External filters generally have a similar effect but are more adjustable, so it is possible to position the return pipe or spray bar to send the water straight down to the tank floor, and this would rapidly wash any food down with it.

Some tanks have filters that are situated in the hood and work by gravity with the water dropping through them and then back into the tank; these can make a fierce downward flow as well. If your filter is pushing water downwards then it can be a good idea to switch the filter off during feeding to prevent this — just be sure to switch it on again afterwards!

Many fish foods have a mixture of densities in the one pack, so some will float, some sink rapidly and some slowly. In theory this should offer most types of fish a chance to feed. It might also be worth considering feeding in smaller quantities so the fish can gobble up most of the food before it reaches the bottom.

Of course any bottom feeding species such as Corydoras will appreciate the food that sinks to the substrate.BOB MEHEN

I have a healthy male Dwarf gourami but I have lost three females, all of which have wasted away. He doesn’t seem to be bullying them — they just seem to become skinny, stop eating and then hang about in one corner of the tank. I’m not inclined to try another, so will he be OK on his own — or should these fish really have a mate?LYNN WOODS, EMAIL

Dwarf gouramis are an old aquarium favourite, and rightly so given the lovely colour displayed by the males. Native to India, Pakistan and Bangladesh, the fish seen in the hobby are largely commercially produced in Singapore. Sadly many of these fish are plagued by a nasty disease known as ‘Dwarf gourami iridovirus’, some of the symptoms of which are similar to those you describe seeing in the females you have lost. This disease is untreatable, but the fact that the male is unaffected could be down to a natural immunity.

However, the males of this species are also well known for bullying and pestering females, especially if the tank is too small or doesn’t offer enough cover in the form of dense vegetation.

Lush floating plants are ideal for this, allowing females to hide away from the male’s unwanted attentions. As you have already lost three females it seems to me that even though you haven’t noticed any bullying it is still the most likely cause of their demise. A well-established healthy male will see each new female as a potential mate and immediately begin trying to impress her, regardless of her condition.

This probably means the new fish have no time to settle in and feed up and simply fade away.

My advice is to keep the male by himself. He won’t suffer from being kept alone and you’ll be able to enjoy his gorgeous colouration without worrying about a harassed and sickly female.BOB MEHEN

A tank that’s heaving with snails could indicate a lack of maintenance.

WORDS: NEALE MONKS

There’s no simple answer to this. A lot depends on how desperate you are to eliminate the snails completely. If you want to get rid of them all, then essentially stripping the tank down, changing the gravel, picking snails off solid objects (including filter media), and very likely replacing all the plants will be part of the answer. Traps of various kinds are on sale as well, and these do work if used correctly. Even then, some will survive, so you’ll need to keep remove any remaining snails as and when you see them. It’s a lot of work, but this approach can succeed if you’re persistent. It’s a lot like weeding a garden: doable, but not something you do once and for all!

Don’t forget snails do little serious harm in fish tanks. They’re unsightly rather than dangerous. Indeed, Malayan livebearing snails do some good by aerating the substrate. It’s perhaps better to think of them as warning signs that your tank has too much organic detritus lying about. A clean tank is, very largely, a snail-free tank. Where you see a lot of snails you’re probably looking at a tank that could do with a tidy up and perhaps stricter maintenance when it comes to removing uneaten food, dead plants and so on.

4 ways to control your snail population

Disinfect your plants: Rinse all new aquarium plants and treat them with an aquarium snail treatment before introduction.

Add a snail eater: Some fish will eat snails, such as Botia loaches and puffers, but they’re not suited to all tanks. Try a snail-eating snail in the form of Clea helena.

Buy a snail trap from your aquarium shop, or make your own using a couple of slices of courgette which can be placed under a saucer in the evening. Remove the snails that collect on it a couple of hours afterwards and repeat.

Bob Mehen has some advice for a reader who's trying to decide between two differently-priced, but similar-looking fish.

Q. I’ve been looking for a couple of suitable catfish for my 350 l/77 gal tank and I’ve decided I’d like to try Synodontis. This is partly because I’ve never kept them before and partly because I understand they come from Africa, which is where the Congo tetra I have in the tank already are from.

Looking around my local shops, I noticed some lovely looking fish labelled 'Clown syno, S. decora' at £35 each, as well as some similar looking but much cheaper fish labelled 'Zebra syno' at just £10 each.

Is there any difference between the two fish, and if so, which would you recommend I buy?

Roger Attwood, email

A. Synodontis are making a welcome comeback to the hobby, having fallen out of fishkeeping fashion in the last 20 years with the rise in popularity of'L' number catfish. However, one of the reasons for their fall from favour was the appearance of man-made hybrids, and sadly, there still seems to be a ready market for these.

The Clown syno you mention was hopefully the lovely Synodontis decorus (or at least that was the name the scientific community had settled on last time I looked), a wonderful fish with beautiful black spot and stripe markings and fin extensions when adult. They are one of the larger species and grow to around 25cm/10in, so they may be a tight fit for your tank when mature.

The 'Zebra syno' is almost certainly a hybrid, which is why its price will be so much lower. While these hybrids are often very attractive looking, their unknown origins make them hard to predict long-term, which can be a worry as many Synodontis are easily capable of living in excess of 20 years. What your bright, spotty bargain will look like in five years is a mystery, and it may turn into a large, dull grey brute thanks to 'hybrid vigour'.

Most of the fish I have seen sold under the 'Zebra' name appear to have S. decorus as one of their parents, but their copper-coloured eyes suggest that the other parent might be a Rift Lake Synodontis such as S. multipunctatus. These fish come from hard, alkaline conditions that are totally different to the often soft, acidic conditions preferred by riverine species like S. decorus. Who knows what water chemistry the hybrid progeny of these two will do best in?

Personally, I’d recommend you steer clear of any fish that is not clearly identifiable as a true species. My recommendation would be a small group of the lovely Pyjama catfish, Synodontis flavitaeniatus, which is a smaller, more sociable fish that would be ideally suited to the size of your tank.

Dave Wolfenden advises a reader on why a Blood shrimp may have made a meal of a smaller tank mate.

Q. My mother has a 90 l/20 gal reef tank that was set up a couple of weeks before Christmas. It contains live rock, a couple of snails, a few hardy coral frags, a Blood shrimp, Cleaner shrimp and an Emerald crab. There are no fish.

Yesterday she saw the Blood shrimp — the bigger of the two shrimp — chase and kill the Cleaner, which it then started to eat. The Cleaner didn’t appear to be ill at all. Both shrimp were added together about three weeks ago.

Is this a regular occurrence — or is it possible they’re not getting enough to eat? The Blood shrimp is out a lot, considering they’re meant to be quite shy — is this because it’s hungry? There are no fish food leftovers for the shrimp because the tank doesn’t have any fish. Instead, they’re fed a few drops of a liquid food called Gamma Nutraplus every other day.

There were remnants of the usual brown algae bloom when the shrimp were first introduced, but that’s gone now. Please could you advise — and will the crab be safe?

N. Young, email

A. Blood shrimp, Lysmata debelius, are generally peaceful and easy-going inverts. They tend more towards scavenging than the cleaning-obsessed Ambon shrimp, L. amboinensis, and generally get on fine with other ornamental shrimp with the exception of, for example, Banded shrimp, Stenopus hispidus, and certain pistol shrimp.

Lysmata have very small claws that make them less equipped than these other big-clawed species to dismember their tank mates. There are occasional reports of Blood shrimp attacking other crustaceans, but it’s not clear why this happens. It may be a territorial dispute, but as I say, most of the time these little shrimp will get on just fine.

It could be an issue with feeding (perhaps the Blood shrimp was simply ravenous), and I suspect that the feed that was being supplied wasn’t sufficient — these shrimp have a surprisingly large appetite. Many aquarists report that Blood shrimp are shy, but some individuals are very outgoing, so it’s difficult to say whether this one was particularly visible due to it being hungry. In any case, I would definitely recommend feeding the shrimp on some small pieces of Mysis or other frozen foods, or even pellets are often eagerly accepted (and this applies to the Emerald crab as well, incidentally).

The Emerald crab shouldn’t be at any risk from the shrimp — they’re much tougher than the spindly, delicate cleaners. However, all crustaceans are vulnerable at moulting. It’s for this reason they assume cryptic behaviour around this time, hiding out until the shell hardens up. The crab should look after itself, but ensure there are plenty of rocky nooks and crannies into which it can hunker down when it’s due to moult. I do, in fact, wonder if the Cleaner was entering a moulting phase, and the Blood shrimp seized the opportunity to have a feast (moulting crustaceans give off pheromones that can be detected by others); it’s a possibility, but hard to say.

On balance, I’d up the feed and avoid adding another Cleaner in view of the Blood shrimp’s track record. Adding another Blood shrimp (with caution) shouldn’t pose any problems, providing they’re well fed.

Is it stressful for a clownfish to be kept without a mate? Dave Wolfenden offers his thoughts to a reader who would like to keep a singleton in a smaller set-up.

Q. If a clownfish is kept singly, does it remain a small male because there’s no other clownfish to trigger a sex change, or does it become female because being an individual, it’s dominant? Also,

is it cruel to keep one clownfish?

I’ve always kept them in pairs, but I would like to keep just one black and white in a smaller set-up. What’s the minimum size for a single?

Jennifer Jacobs, Kent

A. Clownfish have a weird sex life, and they’re referred to as protandrous (male first) hermaphrodites. They all start out as gender-neutral effectively, so they are really neither boys nor girls. They all then develop male gonads, but in a group of clowns, all but two individuals are non-breeders.

The most dominant individual in the group develops female gonads and can breed; the next most dominant individual’s male gonads mature, and he too can breed. However, breeding and gonad development is suppressed in all the other fish due to aggressive interactions from the dominant pair. Fish can shuffle up the hierarchy if one of the dominant pair is removed. For example, the dominant male will become a girl if the dominant female is removed, and the most dominant of the other males will become the breeding male — it’s complicated!

We still don’t fully understand the mechanism of this bizarre strategy, but the aggression from the dominant pair appears to influence hormone levels in the subordinates, and in turn, this affects gonad development as well as growth of the fish (subordinates remaining smaller than the larger dominant male and even larger female). In situations where a single clownfish is maintained on its own, the social interactions to suppress development aren’t there, so they will tend towards becoming female.

Whether keeping a solitary clownfish is cruel or stressful is difficult to answer. Stress is actually a natural part of clownfish life, thanks to the intense, relentless social interactions that maintain the group dynamics. But this a normal part of their behaviour, and if we wish our animals to show the most natural behaviours possible, there’s a case for keeping them in social groups that allow them to do what comes naturally.

I’d suggest that the best way to keep your clowns is in a pair (trying to form larger groups can lead to a lot of aggression and the dominant fish can kill subordinates). A pair will need around 120 l/27 gal. Select fish wisely.

Fully grown specimens can be a recipe for disaster; instead, introduce two small fish that should not have yet reached sexual maturity. They can then pair up naturally and establish themselves.

Captive bred individuals are readily available, and I’d definitely recommend these over wild-caught. Whatever you go for, be sure to quarantine them for 30 days prior to introduction to the aquarium, as parasitic diseases such as Brooklynella can be a real problem with clownfish.

Q. I have a Juwel 240 l/53 gal tank with a Snowflake moray eel, Porcupine pufferfish and a French angelfish. The tank has been set up for 16 months. Recently my Snowflake eel has stopped eating. When I bought it, it didn't eat for five weeks — this coincided with an article you ran on moray eels where you suggested that when introduced to a new tank they may not eat for a while. So at the time I didn't worry. Both the other fish continue to eat as normal. I have tested the water and the ammonia and nitrite are 0ppm and nitrate is very low (15ppm).

The eel has also become much more active and is swimming quickly around the tank at night as well as digging in the gravel and piling the gravel up at the sides of the tank. I have tried feeding it prawns, lancefish, cockles, mussels and even plaice, but he refuses to take it. I am very attached to it and don't want to lose it. Please could you help?

Carol Hussey, email

It is normal for a newly-introduced moray to go on hunger strike for a little while, and these fish can last a surprisingly long time without feeding when first introduced. However, there does appear to be an issue here, and you’re right to take note of the change in the eel’s behaviour — it’s a warning sign that something’s not right. Once a moray starts feeding, it’s pretty rare to see them go off their food for a long time.

One of the most common causes of morays stopping feeding is aggression from unsuitable tank mates, and I think you’ve got a problem here. In fact, I’d suggest that you’re going to have to have a think about the long-term viability of this aquarium.

The first issue is tank size. 240 l/53 gal is just way too small for these fish. Bear in mind that a French angel will grow to at least 30cm/12in in captivity, and whichever species of porcupinefish (Diodon spp.) you’ve got, then you can expect it to reach at least the same size — maybe even a lot more! Secondly, Porcupines and French angels are pretty aggressive, and even smaller specimens can bully and harass tank mates, especially where territory size is limited.

In contrast, Snowflakes have a peaceful demeanour with most fish. I’d put money on the more laid-back moray being the subject of some belligerent behaviour from one or both of its tank mates. The change in behaviour could be a result of this — it seems natural that a stressed, intimidated fish such as this would try to escape from the attention it’s getting, and the digging and gravel rearrangement sounds like an evasive strategy on the part of the eel.

The eel needs to be separated from its tank mates, but you’ll have to plan for the long-term care of the porcupine and angel. I’d suggest that the best option for these two is to be placed in a much larger system. Ideally, you’re looking at 750 l/166 gal minimum for adult specimens of these fish.

The eel will quite happily live in your existing aquarium, and bear in mind that you can keep several in the same tank.

Q. Four months ago I bought a pair of Kribensis, hoping to breed them. The fish in the shop tank were in pairs, but the two fish I got were from two different pairs, and the male is slightly smaller than the female. However, since day one all the female seems to want to do is chase the other fish in the tank, especially the male Kribensis. The second she sees him she zooms after him, and his tail is now in shreds (although he is otherwise healthy). The other fish in the tank are danios and Red eyed tetras.

There are a few caves in the tank, and all the fish are well fed and healthy. Why is this happening and how can I solve it? I would still really like to breed these cichlids.

Jason Roberts (13), email

A. Pelvicachromis species such as Kribs are unusual among cichlids in that both females and males claim their own territories. In the wild, what is supposed to happen is that each female holds a small territory, and within that territory will be a cave or burrow where she keeps her eggs or fry.

Males hold bigger territories that usually include those of several females. He drives away rival males and presumably any potential predators that might eat eggs or fry, but he doesn’t otherwise get too involved in rearing his offspring. In short, Kribs are what are called 'harem spawners', named after the idea of exotic kings who maintained harems of many wives.

In aquaria, Kribs have turned out to be very adaptable and can work as pairs without problems. But usually, what you see is that the female is the more territorial of the two, and often after they have spawned, the female actually drives the male away from her burrow or cave and only allows the male back once the eggs

have hatched.

As the days pass, she becomes a bit more trusting, eventually letting the male look after the fry while she goes off to feed; but I’ve always got the impression that in Krib relationships, it’s the females that call the shots! If she decides to rear the fry on her own then that’s what she’ll do, and the male better have somewhere to hide when she’s feeling protective!

For best results with Kribs, make sure they have lots of hiding places, particularly caves. Each fish wants its own territory, and it may take some time for them to decide to join forces and protect a single cave. Sturdy plants like Anubias and Java ferns can be very useful for creating territorial boundaries. Sometimes you can reset things by moving all the rocks and plants about, forcing the male and female to re-evaluate each other; and if you’re lucky, fish that didn’t get along before might even start being nicer to each other.

If the worst comes to the worst, you could try swapping this male for another one. It may simply be that they aren’t compatible and she’s not willing to accept him.

Neale Monks offers some feeding advice to a PFK reader who wants to vary his fishes' menu.

Q. Is it safe to use food from my fridge-freezer to feed my fish? I’m thinking that seafood should be okay, but what about vegetables and meat?

Henry Eze, email

A. Quite a lot of human food is perfectly safe to use when feeding your fish. White fish fillet is good, particularly Tilapia, cod and coley, but avoid oily fish as that tends to be a bit too messy. Seafood is good, but be careful not to rely too heavily on prawns or mussels because these contain a chemical called thiaminase that breaks down Vitamin B1.

Meat is trickier because it contains fats that cause problems for aquarium fish so is best avoided. An exception is beefheart, which isn’t as fatty as most other meats once the obvious fat is trimmed away, and can be frozen, shredded, and fed to many types of fish without problems. In the past it was often used as a staple for fussy fish like Discus, but this isn’t common now.

Hard boiled egg yolks are another old standby, often used to feed fish fry and baby livebearers. The particles of yolk can make the water cloudy if overused, but many small fish (and shrimps) seem to go wild for egg yolk, so it’s a worthwhile treat now and again.

Green foods are well worth trying, as are some fruits. Blanched lettuce and cooked peas and spinach are enjoyed by most herbivorous fish, while suckermouth catfish like plecs will also happily graze on raw courgette, cucumber and sweet potatoes, even slices of melon!

Some of these green foods need to soften for a few days before the fish will eat them, so don’t be too quick to whip them out if your fish don’t seem to show much interest. It’s also worth noting that herbivorous fish my pass over healthy green foods if they’ve been pampered with protein-rich pellet and flakes, and letting your fish starve a few days may be necessary before they decide to 'eat their greens!'